We are using the 43C9 antibody, which was raised against a phosphonamidate hapten to catalyze the hydrolysis of amide and ester bonds, as scaffold for the design of metal sites with the ultimate goal of designing a site with a catalytically active metal. Differences in side chain positions between the crystallographic structures of native 43C9 and a Zn-binding mutant have been used to identify residues that will the Zn-binding site. In addition, we have been able to model the hapten binding based on the crystallographic structure 43C9-p-nitrophenol binary complex, and used it to identify other mutations that will improve the metal binding site. In the future we hope to explore this Zn-binding site further and to elucidate the structures of other potential catalytic metal binding sites.